A Canadian gun crew performing maintenance of the bore on the 6-pounder.

Limitations of the existing 2 pounders were apparent even as the gun was first entering service, and an effort was made to replace it with a much more capable weapon starting as early as 1938. The Woolwich Arsenal was entrusted with the development. The 57 mm calibre was chosen for the new gun. Guns of this calibre were employed by the Royal Navy from late 19th century, and therefore manufacturing equipment was available. The design was complete by 1940, but the carriage design was not completed until 1941.[citation needed] The production was further delayed by the defeat in the Battle of France. The loss of equipment and the prospect of a German invasion made re-equipping the army with anti-tank weapons an urgent task, so a decision was made to carry on the production of the 2 pounder, avoiding the period of adaptation to production, and also of re-training and acclimatization with the new weapon. It was estimated that 100 6-pounders would displace the production of 600 2-pounders.[2] This had the effect of delaying production of the 6 pounder until November 1941 and its entry into service until May 1942.

Unlike the 2-pounder, the new gun was mounted on a conventional two-wheeled split trail carriage. The first mass production variant—the Mk II—differed from the pre-production Mk I in having a shorter L/43 barrel, because of shortage of suitable lathes. The subsequent Mk IV was fitted with a L/50 barrel, with muzzle brake. Optional side shields were issued to give the crew better protection, but were apparently rarely used.

The 6 pounder was used where possible to replace the 2-pounder in current British tanks, requiring work on the turrets, pending the introduction of new tanks designed to take the 6-pounder from the outset. The Churchill Marks III and IV, Valentine Mark IX and Crusader Mark III all began to enter service during 1942. The Valentine and Crusader both needed to lose a crew member from the turret. Those tanks designed to take the 6-pounder from the outset were the problematic Cavalier and the Cromwell and Centaur. When the Cromwell went into combat in 1944 it was however armed with the Ordnance QF 75 mm gun, which was a redesign of the 6-pounder to take US 75 mm ammunition and more useful against general targets. The 6-pounder was also fitted to the AEC Armoured Car Mark II.

Although the 6-pounder was kept at least somewhat competitive through the war, the Army nevertheless started development of a more powerful weapon in 1942. Their aim was to produce a gun with the same general dimensions and weight as the 6-pounder, but with improved performance. The first attempt was an 8-pounder of 59 calibre length, but this version proved too heavy to be used in the same role as the 6-pounder. A second attempt was made with a shorter 48 calibre barrel, but this proved to have only marginally better performance than the 6-pounder. The program was eventually cancelled in January 1943.

Instead the 6-pounder was followed into production and service by the next generation British anti-tank gun, the 17 pounder which came into use from February 1943. As a smaller and more manoeuvrable gun, the 6-pounder continued to be used by the British Army not only for the rest of World War II, but also for some 20 years after the war.

A 57/42.6 mm squeeze bore adaptor was developed for the gun but was never adopted.

The idea of manufacturing the 6 pounder in the U.S. was expressed by the U.S. Army Ordnance in February 1941. At that time the U.S. Army still favored the 37mm Gun M3 and production was planned solely for lend lease. The U.S. version, classified as substitute standard under the designation 57 mm Gun M1, was based on the 6 pounder Mk 2, two units of which were received from the UK. However since there was sufficient lathe capacity the longer barrel could be produced from the start.[3] Production started early in 1942 and continued until 1945. The M1A1 variant used US "Combat" tyres and wheels. The M1A2 introduced the British practice of free traverse, i.e., the gun could be traversed by the crew pushing and pulling on the breech, instead of solely geared traverse, from September 1942. The M1 was made standard issue in the Spring of 1943.

A more stable carriage was developed but not introduced. Once the 57 mm entered US service a modified towing point design was introduced (the M1A3) but only for US use. Tractors for the M1 include the Dodge WC-63 11⁄2-Ton 6x6 and the White Half-Track.

Two-thirds of American production (10,000 pieces) went to US Army Divisions in Europe. About one-third of production (over 4,200 pieces) was delivered to the UK and 400 pieces were sent to Russia through Lend Lease. When the United States re-armed and re-equipped Free French forces for the Normandy landings, their Anti-Tank units received American-made M1s.

Like the British Army, the U.S. Army also experimented with a squeeze bore adaptor (57/40 mm T10), but the program was abandoned. American shell designs and production lagged behind the introduction of the gun once it was accepted for service and so at first only AP shot was available. The HE shell was not available until after the Normandy landings and UK stocks were procured to cover its absence.

Its use by regular US Army front-line units was discontinued in the 1950s.

A 6-pounder anti-tank gun and its crew in action in the Western Desert, November 1942

A gun of 86th Anti-Tank Regiment prepares to fire during a practice shoot at the Royal Artillery ranges, September 1942

The 6-pounders (and the U.S.-built M1, of which 4,242 pieces were received) were initially issued to the Royal Artillery anti-tank regiments of infantry and armoured divisions in the western theatres (four batteries with 12 pieces each), and later in the war to the six-gun anti-tank platoons of infantry battalions. An airlanding battalion had an AA/AT company, with two four-gun AT platoons. The Far East theatres had lower priority and different organization, reflecting lower tank threat. The gun was also employed by Commonwealth forces, in formations similar to the British ones. Initially the anti-tank ammunition was a basic Armour-Piercing (AP) shot, but by January 1943 an Armour-Piercing, Capped (APC) shot and an Armour-Piercing, Capped, Ballistic Capped (APCBC) shot was supplied. A High Explosive shell was produced so that the gun could be used against un-armoured targets as well.

The 6-pounder first saw action in May 1942 at Gazala. It made an immediate impact on the battlefield as it was able to penetrate any enemy tank then in service. In the most celebrated action, the 6-pounder guns of 2nd Battalion, The Rifle Brigade (together with part of 239 Anti-Tank Battery Royal Artillery under command), destroyed more than 15 enemy tanks in the action at 'Snipe' during the Second Battle of El Alamein. However, over the next year the Germans introduced much heavier designs into service, notably the Tiger I and Panther. The standard 6-pounder shot was ineffective against the front armour at any range, but proved effective on the less armoured sides and rear armour. It was the 6-pounder gun that accounted for the first Tiger disabled in North Africa; its projectile jammed the Tiger I turret. The situation was somewhat improved by the development of more sophisticated ammunition, in the form of the Armour-Piercing, Composite Rigid (APCR) shot, and the Armour-Piercing, Discarding Sabot (APDS) shot, which was available from 1944 and made it effective in fighting the Tiger I and Panther tanks frontally.

The first tank to go into action armed with the 6 pounder gun, was the Mark III version of the Churchill tank, in the disastrous Dieppe Raid of August 1942. They were deployed to North Africa and eight were in action at El Alamein in October. It was a 6 pounder armed Churchill which was the first western tank to knock out a Tiger I in tank vs tank combat in April 1943. In the Royal Artillery regiments, the 6-pounders were joined by the 17-pounders starting in 1943, but in infantry units the gun remained the sole AT gun in service until 1951, when it was finally declared obsolete and replaced by the 17-pounder in the British Army of the Rhine (BAOR).

The Royal Navy used the 6-pounder extensively in Motor Gun Boats during World War II (especially the 'D' type). The gun was mounted on a hydraulic-powered mount and fitted with the Molins power loading system, permitting a six-round burst at one round per second. The guns were all the early short-barrel (43 calibre) type, and fired exclusively HE (high-explosive) ammunition, at much lower muzzle velocities than for AP (armour-piercing), because of the use of flashless propellant for night operations. The naval designation was QF 6-Pounder Mk IIA; nearly 600 of these weapons were made.

The Molins autoloader was also deployed for a short time on some Royal Air Force de Havilland Mosquitos of Coastal Command, which were referred to as the "Tsetse" (after the biting fly). Officially the QF 6pdr Class M Mark I with Auto Loader Mk III, it was based on the long-barrelled (50 calibre) gun. It was fully automatic, with a rate of fire of about 55 rounds per minute, with an ammunition supply of 21 rounds. It was intended for use against U-boats and could still penetrate their hulls through 2 ft (61 cm) of water. It was replaced by the more versatile but less accurate 3-inch Rocket Projectile when it became available in 1943.[4]

In spring 1943, following the experience of the North African Campaign, the Infantry branch of the U.S. Army recognized the need to field a heavier antitank gun than the 37 mm M3. According to the Table of Organization and Equipment (TO&E) from 26 May 1943, a regiment antitank company included nine 57 mm guns and each battalion had an antitank platoon with three guns giving a total of 18 guns per regiment. Dodge WC-62/WC-63 6×6 1½ ton trucks were issued as artillery tractors in place of the 3/4 ton truck used with its predecessor the 37mm. Introduction was made in the face of objections by the US Army Infantry Board which believed it too heavy. The Ordnance Board on the other hand felt a more powerful weapon should be introduced; Airborne and Cavalry rejected it. By mid-1944 the M1 was the standard antitank gun of the U.S. infantry in the Western Front and outnumbered the M3 in Italy.

Because of the unexpected adoption for service, the only ammunition type in production in the U.S. by mid-1943 was the AP ammunition. Only after the Normandy Campaign did the HE round reach battlefield (U.S. units were sometimes able to get a limited amount of HE ammunition from the British Army), and the canister shot was not seen in significant numbers until the end of the war. This limited the efficiency of the gun in the infantry support role. Also, APCR or APDS rounds were never developed by the US. Canister round production did not start until early 1945 and was also in limited use. Some British stocks of APDS were supplied to the US units.

The Airborne Command had rejected the 57 mm M1 in the summer of 1943 claiming it was unfit for airlanding by glider due to its weight and the TO&E of February 1944 still had airborne divisions keeping their 37 mm guns. Nevertheless, the 82nd and the 101st airborne divisions were re-equipped with British-manufactured 6 pounders on the narrow carriage Mk III designed for glider use—24 in AA battalion, and 9 in glider infantry regiment—for the Normandy airdrops. The use of the British 6 pounder with the MK III carriage was again used by the 442 AT Company as part of the glider invasion force assigned at that time to the 517th Parachute Infantry Regiment, First Airborne Task Force, during Operation Dragoon; the invasion of Southern France. Subsequently the guns were officially introduced under the TO&E from December 1944. According to the TO&E, a division was issued a total of 50 pieces: 8 in divisional artillery, 24 in AA battalion, and 18 in glider infantry regiment; parachute infantry regiments did not have anti-tank guns. The British guns were referred simply as 57 mm guns.

Canadian troops man a 6-pdr anti-tank gun during Exercise 'Spartan', 9 March 1943

In the fighting after the Normandy landings the paratroops used them against German armour near St Mere Eglise and Carentan. However few tanks were encountered and they were mostly used for support which made the shortage of HE shell more significant. From July, US anti-tank units encountered the Panther tank which was only vulnerable to the 57 mm from the sides. Towed anti-tank guns were less effective in the hedgerow terrain where mobility suffered but when the Germans went on the offensive in August they were effective in defence with infantry. Towards the end of the war, towed anti-tank units were out of favour due to their lack of mobility compared to self-propelled guns and the 57mm was used by infantry battalions. However with few tanks to contend with some units that would have been equipped with the 57mm were instead deployed as rifle companies or only with the Bazooka.[5] The M1 went out of service in the U.S. soon after the end of the war.

In addition to being used by the U.S., British and commonwealth forces, the M1 was supplied under the lend lease program to the Free French Forces (653), USSR (400) and Brazil (57). The Israel Defense Forces employed the 6-pounder in the 1950s in brigade-level anti-tank battalions and battalion-level anti-tank platoons (the latter formations were disbanded in 1953). By late 1955, Israel Defense Forces possessed 157 pieces and 100 more were purchased from the Netherlands in 1956, too late to enter service before the Suez Crisis. Some of those are described as "57-mm guns, nearly identical to the 6-pounders and firing the same ammunition", which apparently makes them U.S.-built M1 guns.[6] The gun was also used by the Pakistani Army; numerous examples can still be seen as 'gate guards' outside army bases in Pakistan. The Irish Army acquired six 6 pounder anti-tank guns in the late 1940s. The U.S. 57 mm M1 gun is popular with modern-day cannoneers, as there is a relatively good supply of shell casings and projectiles. The gun is also reportedly still in active military use with some South American countries, and in coastal defense emplacements of outlying island garrisons of the Republic of China Army.

Mk 2: first mass production version. Shortened L/43 barrel was adopted due to the shortage of suitable manufacturing equipment.

Mk 3: tank version of Mk 2.

Mk 4: L/50 barrel, single baffle muzzle brake.

Mk 5: tank version of Mk 4 .

Molins Class M gun: 6 pounder gun fitted with automatic loader built by the Molins company, a manufacturer of cigarette making machines. It was mounted on the Royal Navy Motor Torpedo Boats and in the RAFMosquito planes, which were referred to as the "Tsetse".

57 mm Gun M1: U.S. built version; although based on Mk II, it had the "original" L/50 barrel.

Carriage types, British:

Mk 1

Mk 1A: different axle and wheels

Mk 2: simplified design

Mk 3: modified for use by airborne troops

Carriage types, U.S.:

M1

M1A1: U.S. wheels and tyres

M1A2 (1942): improved traverse mechanism, allowing free traverse

M1A3 (1943): modified towing hook; the first version to be adopted by the U.S. Army